1. Field of the Invention
The present invention relates to image processing for rendering an image by using a ray-tracing method.
2. Description of the Related Art
The ray-tracing method is often used in computer graphics (CG) as a means for obtaining a realistic rendering result. The ray-tracing method traces the trajectory of a ray reaching a light source by tracing back the path of the ray from a view point in the reverse direction. When tracing back a ray for every pixel to be rendered, its execution requires an enormous processing time. For this reason, there is available a technique of executing ray-tracing method for part of a rendering area.
There has also been proposed a spectral ray-tracing method which reproduces the physical behavior of light to further approximate a rendering result to an actual scene. Spectra express light and are constituted by light beams having various wavelengths. The spectral ray-tracing method can reproduce scattering by a prism, structural colors from an optical disk, the rainbow luster of pearls, and the like by tracing back a ray for each wavelength of light. In addition, there is available a technique of performing RGB display of the calculation result obtained by the spectral ray-tracing method by using color matching functions and the like.
Assume that the spectral ray-tracing method traces back a ray by performing sampling in increments of 10 nm in the wavelength range of 380 nm to 740 nm in the visible range. In this case, it is necessary to trace back a ray 36 times per pixel. That is, the processing time in the spectral ray-tracing method is at least 36 times that in the ray-tracing method, and hence it is difficult to finish the processing within a practical time.